The invention relates to an electrode arrangement for electrothermal treatment of the human or animal body, and in particular to electrocoagulation.
The application of high-frequency alternating currents (specifically in the frequency range of between 300 kHz and 2 MHz) to generate high temperatures for tissue coagulation as a surgical procedure has long been known. In practice monopolar or bipolar electrode arrangements are used for introducing the HF-current into the tissue.
In the case of the monopolar arrangements, an electrodexe2x80x94also referred to as the neutral electrodexe2x80x94is designed in the form of a patient delivery line of large area and fixed to the patient not too far away from the point of intervention and earthed or connected to ground. A second electrode which is manipulated by the operatorxe2x80x94also referred to as the active electrodexe2x80x94is connected to the alternating current generator. In terms of its shape, the second electrode is selected to be adapted to the respective use involved, in particular the size of the tissue region to be treated, in such a way that both the operational time and also the thermal loading of the region of the body or organ involved are reasonable.
In the case of arrangements for bipolar HF-surgery, both electrodes are connected to the HF-generator and are of mutually comparable dimensions, and are placed by the operator in the immediate proximity of the intervention location and are generally both guided actively. Bipolar electrode arrangements are also known in which both coagulation electrodes are arranged on a catheter.
WO 97/17009 discloses a bipolar electrode arrangement with a fluid duct, by way of which flushing fluid can be introduced into the operational area.
WO 96/34569 and the documents referred to in the international search report disclose systems and processes for the ablation of body tissue while maintaining a pre-calculated maximum tissue temperature, in which fluid cooling or thermoelectric cooling is provided during the actual tissue coagulation procedure. Those known arrangements are intended for the introduction into body cavities by way of natural accesses.
The object of the present invention is to provide an electrode arrangement which permits quick and easy interstitial tissue coagulation even in relatively treatment regions.
The present invention includes the basic teaching that the electrode arrangement is mechanically designed in such a way as to facilitate direct penetration into body tissue and at the same time thermal means are provided for setting an advantageous effective temperature profile for the insertion phase.
That notion is based on the fact that the known arrangements which are cooled during the actual electrothermy procedure have admittedly afforded many advantages, but they are not well suited to being inserted into body tissue directly (invasively), with duct formation, for interstitial use. For that reason, in clinical practice, in many cases a duct to the treatment region is firstly opened with a separate incision instrument and in an additional working step on the part of the operator, before the electrothermy applicator is advanced in the duct.
It is further based on the realization on the part of the inventors that a xe2x80x9ccoldxe2x80x9d applicator can be inserted with more difficulty than one which has been warmed somewhat.
A short-term temperature control procedure to a temperature above about 30xc2x0 C., more especially somewhat above body temperature, has proven to be advantageous for the insertion phase. As soon as the applicator has reached the treatment location and the actual electrothermal treatment is initiated, the procedure involves implementing a transition to adjusting an effective temperature profile which is optimized in regard to optimum coagulation performance. Even in periods of time of that phase, heating in addition to the generation of heat by way of the electrodes can be desirable.
In a particularly effective, and at the same time inexpensive embodiment, the electrode or electrodes, or the electrode carrier, are provided with a cavity which is closed off in relation to the body and which is connected to a fluid source which can be the subject of temperature control within a predetermined range so that the suitably temperature-controlled fluid flows through the electrode or the carrier thereof.
Distilled water is preferably used as the fluid, having regard to the low costs involved and the simple and safe handling thereof. In addition, for specific situations of usexe2x80x94possibly having regard to specific safety precautionsxe2x80x94it is also possible to use other fluids which have proven their worth as heat-transfer agents, such as, for example, compressed air, carbon dioxide or silicone oil.
In another possible embodiment the electrode or the electrode carrier has a thermoelectric heating and cooling device which can be, for example, in the form of a combination of resistance heaters and Peltier elements.
In an embodiment which is simple to produce and handle, the electrode carrier is preferably a tubular, in particular cylindrical, element of electrically insulating material, on the peripheral surface of which is or are arranged one or more electrodes and in the interior of which is arranged the temperature control device. To facilitate penetration into the tissue, the electrode carrier desirably has a distal end which decreases or tapers to an approximately conical tip, and the electrodes are fitted substantially flush into the peripheral surface of the carrier.
In the preferred embodiment, in the form of a bipolar arrangement, the assembly includes two electrodes which are mounted to one and the same electrode carrier, in particular in an axial row. In that case, a common temperature control device is provided for both electrodes, such as, for example, the above-mentioned internal tube counterflow temperature control device.
In the preferred embodiment of this alternative configuration, the carrier element is of a cylindrical cross-section, while the two electrodes are of a hollow-cylindrical design and are arranged coaxially with respect to the longitudinal axis of the carrier element. For that purpose the electrodes can be disposed for example in the form of a metallic coating on the surface of the carrier element or each comprise a metal sleeve (for example of titanium or Nitinol) which is pushed onto the carrier element or better inserted flush and forms therewith a press fit.
In a particularly simple embodiment of this arrangement, which is safe and secure in terms of handling, axial fixing of the electrodes is not effected by a continuous carrier element, but by a hollow connecting element which connects the electrodes (which are also hollow) together at their ends. Besides axial fixing of the electrodes, the connecting element also performs the function of insulating the two electrodes relative to each other and it therefore comprises an electrically insulating material, preferably PEEK (polyethyletherketone). The electrodes, the connecting portion and the supply line for the cooling agent (for example a relatively stiff PTFE-hoze which at the same times serves as a handle or gripping portion) are preferably annular or tubular and are of the same cross-section so that the surface of the catheter is a closed cylindrical configuration, whereby insertion into the body is facilitated and at the same time unwanted current density peaks can be substantially avoided.
In an alternative configuration of the preferred bipolar arrangement, which can be used in a particularly variable fashion, but which is more expensive in regard to structure, the axial spacing between the two electrodes is adjustable in order to be able to additionally vary the current density distribution and thus the heating output distribution. If the insulator length between the two electrodes in the axial direction is, for example, less than double the electrode diameter, it is advantageously possible to produce spherical coagulation necroses whereas the shape of the coagulation necroses with greater insulator lengths is rather oval.
The geometrical configuration of tissue coagulation can be substantially influenced by the temperature control effectxe2x80x94specifically by the choice of heating/cooling in a given sequence in respect of time.
In a preferred embodiment, besides the electrode or electrodes and the actual cooling device, an electrosurgery apparatus, which makes use of the invention, includes control means for establishing an advantageous effective temperature profile in the treatment region. The control means include, in particular, an effective temperature profile control device for controlling the heating or cooling output and/or the spatial distribution thereof, said control device being connected to the cooling device by way of a control signal connection for supplying a heating and/or cooling output control signal.
The effective temperature profile control device can also be adapted to produce and supply a heating output control signal for controlling the alternating current power and/or the spatial distribution thereof, and can be connected to the alternating current source by way of a control input so that, besides the cooling device, it can also control the HF-sourcexe2x80x94acting as a xe2x80x9cheating devicexe2x80x9d in the tissue. That provides for particularly flexible control of the treatment regime in the event of longer-duration intervention procedures.
The effective temperature profile control device preferably includes an interactively programmable calculation unit for determining simulated time-dependent effective temperature profiles on the basis of parameters of the tissue and the electrode arrangement and assumed parameters of the alternating current source and the heating or cooling device and for effecting a variation in the assumed parameters to ascertain an optimized effective temperature profile. In practice, use will be made of a PC with which the spatial temperature distribution and optionally the time-dependency thereof can be determined and on the screen of which the simulated effective temperature profiles can be represented as an image. That already makes it considerably easier for the operator, prior to an intervention procedure, to select a suitable combination of control values of the temperature control device and the HF-source.
Placing at least one temperature sensor, which responds with a low level of inertia and which is connected to an input of the effective temperature profile control device, at a predetermined position relative to the electrode arrangement in the body, in particular at an electrode or the electrode carrier, makes it possible to implement verification or rescaling of a simulated effective temperature profile during the intervention. The parameters which are to be used in the further course of the treatment can, therefore, be freshly adjusted at any moment in time.
Additional possible options in that respect are afforded by the provision of a device for ascertaining (especially in time-dependent fashion) the heating or cooling output produced by the temperature control device or a value influencing the heating or cooling output, and a device for ascertaining the alternating current power outputted by the alternating current source, or a value influencing such current power.
Insofar as the effective temperature profile control device preferably has means for determining and storing a time-dependency of the cooling output control signal and/or the heating output control signal and for outputting the respective control signal in accordance with the stored time-dependency, a treatment which is established in advance in terms of the operations to be performed by the operator can take place substantially automatically, in regard to the control values. It will be appreciated in that respect that current changes in the control values still remain possible so that the operator can also react flexibly to unforeseen events. As changes of that kind can be detected and can be incorporated into an updated simulation calculation, the consequences for further progress of the intervention procedure can in turn be made clear to the doctor in a virtually real-time mode.